The subject invention relates to an apparatus and method for feeding print media from a stack. (By print media herein is meant items including, but not limited to, sheets, folded inserts, envelopes, postcards and similar items which are comprised in mail pieces.) More particularly, it relates to a method and apparatus suitable for a high capacity feeder capable of handling stacks of up to several hundred print media.
Feeders are well known devices which serve to separate single items from a stack of print media and feed them forward for further processing by apparatus such as copiers, printers and mail processing equipment.
(Those skilled in the art will recognize that feeders generally will be used with a singulation mechanism to assure that only a single sheet at time is fed forward for processing. While necessary for high reliability operation such singulation mechanisms are substantially independent of the sheet feeder and form no part of the subject invention.)
While feeders of various types have generally performed satisfactorily to feed sheets of various types of paper stock, envelopes, and other similar items, a problem has existed in the prior art with regard to the provision of a high capacity multi-media feeder for feeding various items which vary in thickness, weight and other characteristics. As items are fed from a stack it is clearly necessary to provide some mechanism to maintain contact between the feeder mechanism and the stack as items are fed forward and the stack diminishes. This can be most simply accomplished by providing some form of spring driven mechanism which will continuously urge the stack towards the feeder mechanism. While such spring driven mechanisms are inexpensive and simply constructed they do not provide a constant force between the stack and the sheet feeder mechanism over the long range of travel and various types of media inherent in a high capacity multi-media feeder. The varying force between the feeder mechanism and the stack greatly complicates the design of the feeder mechanism; to the extent that, in general, such relatively simple mechanisms for advancing a stack of sheets have not been satisfactory for high capacity feeders, particularly for high capacity feeders intended for feeding various types of print media thick sheets such as envelopes folded sheets, post cards and the like.
Another approach used in feeders in the prior art has been the use of some sort of demand drive mechanism to advance the stack to the feeder mechanism. As sheets were fed from the stack some form of sensor would detect the need for the stack to advance and would generate a signal to the system controller which in turn would activate a motor to energize a mechanism for advancing the stack forwards to the sheet feeder mechanism until the sensor no longer detected the need to advance the stack. Such feeders, however, are generally expensive and require sophisticated sensors, motors and controls to operate.
Accordingly it is an object of the subject invention to provide an improved high capacity sheet feeder.